This application is based on and incorporates herein by reference Japanese Patent Application No. 2002-033691 filed on Feb. 12, 2002.
The present invention relates to a motor having a grounding structure for reducing radio noise that appears at a motor yoke.
In a direct current (DC) motor having a brush, radio noise is produced by friction between the brush and a commutator when the motor is in operation. The radio noise that appears at a yoke of the motor may affect to peripheral devices. To reduce the radio noise, the motor yoke needs to be grounded. Therefore, such a motor includes a terminal made of a conductive elastic material between the motor yoke and an end plate that is arranged adjacent to an opening of the motor yoke. To ground the motor yoke, the terminal is connected to a negative terminal of a power supply or the negative terminal is inserted between the motor yoke and the end plate.
Since the terminal is added, an overall parts cost of the motor increases. Moreover, the connection between the motor yoke and the end plate becomes loose when an external force is applied to the motor or vibration is produced in the motor. If the negative terminal is inserted between the motor yoke and the end plate, the electrical connection between the negative terminal and the motor yoke may become loose.
The present invention therefore has an objective to provide a motor having a grounding structure for reducing radio noise that appears at a motor yoke without any increase in parts cost. A motor of the present invention includes a substantially cylinder-shaped motor yoke, an end plate provided adjacent to an opening of the motor yoke, and a DC power input fixed to the end plate. The motor yoke has a flange at its opening end. The flange protrudes outward and has a contact with a part of a negative terminal of the DC power input section.
In this motor, the motor yoke is grounded via the negative terminal, that is, an additional part is required for grounding the motor yoke. Therefore, the radio noise that appears at the motor yoke is reduced without an increase in parts cost. Moreover, the negative terminal is directly connected to the motor yoke. This maintains the contact resistance between the negative terminal and the motor yoke at low level. Therefore, the radio noise that appears at the motor yoke is constantly reduced.
The negative terminal has an elastic contact segment that protrudes toward the flange. The elastic contact segment is pressed against the flange. Therefore, the contact between the negative terminal and the motor yoke is maintained even when the connection between the motor yoke and the end plate becomes loose.